1. Field of the Invention
The present invention relates to a light beam focus control apparatus and optical disk apparatus and, more particularly, to a focus control apparatus and optical disk apparatus which discriminate waves reflected by a recording/reproducing layer surface on an optical disk and a light-transmitting layer surface (optical disk surface) and adjust the focus of a light beam.
2. Description of the Related Art
Optical disk recording/reproducing apparatuses using optical disks are recently becoming very popular. As the recording information density increases, the light beam focus control technique requires a higher precision.
One of optical disk focus control references is Jpn. Pat. Appln. KOKAI Publication No. 4-123321. This prior art prevents erroneous focus servo control on a light-transmitting layer surface (optical disk surface) in servo control. For this purpose, AGC (Auto Gain Control) operation is restricted to keep the gain at a predetermined position or less during focus servo control operation. The light-transmitting layer surface (optical disk surface) and recording/reproducing layer surface can then be reliably recognized. This realizes high-precision focus control and enables recording/reproducing processing with respect to a high-density optical disk.
When the focus sum signal is at almost the same level between the light-transmitting layer surface (optical disk surface) and the recording/reproducing layer surface, waves reflected by the light-transmitting layer surface (optical disk surface) and waves reflected by the recording/reproducing layer surface cannot be discriminated by a method using the conventional apparatus. The focus is erroneously adjusted to the light-transmitting layer surface (optical disk surface).